Emergency telephone system



April 4, 1944. c, s, o ps 2,346,115

EMERGENCY TELEPHONE SYSTEM Filed June 12, 1943 2 Sheets-Sheet 1 I ISgflalfgalgflb? flunk res non 2 Lines I gnormal voltage I to I F328 1 4L? I responswe to abnormal voltage To -arzotlzer RBI."

Serving as I an, Emergency Centnwl Office INVENTOR BY 0 6' Blwads April4, 1944.

C. S. RHOADS EMERGENCY TELEPHONE SYSTEM Filed June 12(1943 2Sheets-Sheet 2 INVEN-TOR E BY Cliliiwads 2 V TOR EY Patented Apr. 4,1944 EMERGENCY TELEPHONE SYSTEM Charles Stanley Rhoads, Albany, N. Y.,.assignor to American Telephone and Telegraph Com- :pany, a corporationof New York Application'zlune 12, 1943, Serial No."490,567

6 Claims.

This invention relates .to a telephone system in which a plurality ofprivate branchexchanges areconnected to a central oiiice, andparticularly to means, in such a system, by which communication may beestablished between one private branch exchange and the others intheevent of the destruction of the normal signaling means between thecentral ofiice and the private branch exchanges.

In a normal telephone system comprising a central office and a plurality.of private branch exchanges (hereinafter referred to as P. .B. Xs) theringing current for signaling between the P. B. X and a centraloffice orstationsis supplied by .a source at the central office. In the event ofthe destruction of such a central office or the destruction of thecircuit over which such current is supplied to the P. B. Xs, a"P."B. Xwould be unable to communicate with "other central ofiices or otherstations. If the P. 'BL'X thus affected is one that furnishescommunication to a community agency that is vitally necessary for thedefense or welfare of a community, such as the fire department or thepolice department of such community, the matter of providing emergencyservice isoi the greatest'importance.

The present invention resides in an. arrangement of a telephone systemby which, in the eventof the destruction of the source ofringingcurrent, upon which the various PJB. Xs depend for their signalingcurrent, communication may be established between one of the. P. B. Xsacting as an emergency central oifice and certain P. B. Xs-that areassociated with the vitally important agencies of the community in whichthey are located.

This invention will be clearly understood from the following descriptionwhen read in connection with the attacheddrawingso'f whichlFigure 1shows schematically the .manner in which. a telephone system embodyingthis invention is arranged, and Fig. 2 .shOWs .in detail the circuitarrangements and apparatusfor carrying out the invention.

Fig.1 shows asystem in whichthe central-office l is connected bytrunklinestothePfBiXs 2 and 3.and to .other,P..B..X s ,similar'to '3.'The connection between the. central .dfiiceandPijBl'jX 2 is effected.by the trunk. 4 whichterminates at the office and at the P. B. TX in ajack which is equipped in the usual manner. The trunk 5 that connectsthe centralofiice tothe P. .B. X 3 is looped througha jackTinPIBIX'IZ'anditerminates .at 'P. B. Xfi3jin a jack, .not shown in thisfigure. The trunk is equipped at thelatter invention is shownmoreclearly in Fig. 2.

P. B. X with two types of signal apparatus'one of which is responsive tonormal signaling voltage, and the other signalingapparatus'responsive toan abnormal voltage, the latter being essential in the event of the lossof the "battery supply-by which the normal signaling apparatus isoperated at that P. B.'X. At the P. B. X 2, in addition to the apparatusnormally included in a standard P. B. X, there is included-a source ofabnormal ringing Voltage which may be applied to all lines that arelooped through that 'P. B. X when an emergency arises that makes suchaction necessary. For example, if the central. cifice l were destroyed,or the lines leading therefrom were severed, the operator at the P. B. Xz -upon becoming aware of such failure, could'apply the abnormal voltageof her ringing "generator to that portion of the trunk line 5 extendingto the P. B. X 3by inserting the plu '8 in the jack 1. That abnormalvoltage would causetheoperation of'the signal apparatus at P. B. X-3,'which is responsive to the abnormal voltage, and enahlecommunication to "be established betweentwo P. B. Xs in a manner thatwillbe fully described hereinafter.

In such a system the P. B. X' Z serves as an emergency central ofiicethrough which loop the trunks, suchas Sand-6 that serve P. B. Xs,:suchas '3, and others which afford communication to the vital agenciesof' the community.

Thedetailed arrangement ,for' carrying out this In that figure thecentral ofiice I, which would'be a typical central Uffice, isrepresentedby a plurality of jacks l2, l3 and M withwhich any of a plurality ofcord circuits such as the circuit!) is designed to co-act.Associated-withthat cord circuit is a sourceof alternating voltageHlwhich,

for example-maybe of 105'volts'a'nd 20 cycles superimposed upon thedirect voltage of the battery ll. The jack [3 serves to terminate thetrunk 5 that extends from the central ,ofiice to the P. B. ,X 3,'whichtrunk is'looped through :the emergency-key IS in the'P. B. X2. When thatkey is in its normal position the trunk circuit continuous between thecentral office and the P. B. X '3, but when the ke is'operated, suchcontinuity is broken, and that portion of the "trunk'E'betWeen P. B. X 2andP.B.'X 3'willbe terminated upon the springs of the jack [6 at P. B. X2. The cord circuits'atP. "B. X Zyone of which is shown schematicall by26,-are-connected to two sources of ringing-currentthrough a key such asIT. The inner-contactsof that key are connected bya trunk to a source*oiringing current of the normal voltage located in the central ofllce.The outer contacts of key H are connected to a circuit containing amagneto I 8 and source of direct voltage I9 which may, for example, beof 45 or 90 volts, the peak voltage of which is substantially greaterthan that provided by the source at the central office.

At P. B. X 3 the trunk terminates in a jack which constitutes theregular trunk appearance at that P. B. X. Connected between one side ofthe trunk and the uppermost contact of the jack is one of the windingsof the rela 2!. This relay has associated with it another windin and alamp 22, the function of all of which will be later apparent. Alsoconnected across the trunk 5 is a circuit containing the cold cathodetubes 23 and 24 and an emergency ringer 25, which tubes and ringerconstitute the signal apparatus responsive to the abnormal voltageproduced by the magneto I8 and battery 19 associated with P. B. X 2.

The manner in which those circuits operate under normal and underemergency conditions is as follows: signaling between the central ofiiceand the P. B. X 3 will normall be carried on by inserting the plug of acord in the jack l3 and operating the ringing key. Since the key I 5 atP. B. X 2 is in its normal unoperated position,

.the ringing current will pas over the trunk to P. B. X 3 and, flowingthrough the left-hand winding of relay 2|, would cause the operation ofthat relay, closing the locking path through the right hand winding, andin turn causing the lighting of the lamp 22. Upon the receipt of thatsignal the operator would insert the plug of a cord in the jack 26,which would open the circuits of both windings and would extinguish thelamp. The connection between the trunk and the desired station of the P.B. X would be made in the usual manner.

Signaling between the central office and P. B. X 2 would be accomplishedin a similar manner by inserting a plug of a cord such as 3 in the jackl2 and by applying ringing current to the trunk 4 which would operatethe normal signaling apparatus in P. B. X 2 similar to that justdescribed in connection wiht P. B. X 3. Ringing current of normalvoltage to enable P. B. X 3 to signal its own stations would be suppliedto that P. B. X by a trunk, not shown, but similar to that by whichringing current is supplied to P. B. X 2.

If the source of ringing current is cut off from the P. B. Xs by thdestruction of the central office or of the trunk lines over which suchringing current is fed to the P. B. Xs, the operator at P. B. X 2 wouldcommunicate in the following manner with those P. B. Xs whose trunklines loop through P. B. X 2. For example, in order to establishcommunication with P. B. X 3, the operator at P. B. X 2 would operatethe key l5, and thereby would connect to the jack l6 that portion of thetrunk line 5 that lies between P. B. X 2 and P. B. X 3. She would theninsert the plug of a cord circuit, such as 26, into jack I6 and wouldoperate key I! so as to connect across the cord circuit the emergencyringing circuit containing the magneto l8 and the battery l9. Thatringing circuit provides a voltage in excess of the normal voltage, theabnormal voltage being sufficient to break down and to cause a flow ofcurrent through th cold cathode tubes 23 and 24, which, in turn, willcause the operation of the ringer at the P. B. X 3.

Upon receiving that signal, the operator at P. B. X 3 would insert oneof the plugs of her cord circuit into the jack 20. Since the current forher transmitter is sent from the central office I over a special trunkto P. B. X 3, her trans mitter would not function in the event of thedestruction of the central ofiice or of the trunk circuit over which thetransmitter current is supplied, which is the situation that has beenassumed in describing the system with which the present invention isconcerned. In order to talk to the operator at P. B. X 2 the operator atP. B. X

3 would then insert the other plu of the aforesaid cord circuit into ajack connected to one of the extension stations of P. B. X 3 and wouldthen go to that station and use the transmitter at that station to talkto the operator at P. B. X 2. Such communication is possible because thetransmitter at the extension station receives its current from thebattery 21 of the cord circuit 26 which battery is kept charged eitherby a connection to the central office or a local power plant. Thecurrent from battery 21 is not effective for the operation of theoperators transmitter at P. B. X 3 because the circuit of thattransmitter is so arranged as to be energized only by the currenttransmitted by a special trunk from the central office l, as mentionedhereinbefore.

If the operator at P. B. X 3 wanted to talk to the operator at anotherP. B. X associated with another essential emergency agency, the operatorat P. B. X 2 would plug the other cord of the pair connected to thetrunk from P. B. X 3 into a jack associated with the trunk to the otherP. B. X and would ring over the trunk line extending to the other P. B.X, as for example, that represented by 6 of Fig. 1. That would cause theoperation of a ringer similar to 25 at the said other P. B. X, and wouldthereby bring the operator at that P. B. X into communication with theoperator at P. B. X 3.

Since the cold cathode tubes 23 and 24 require a higher breakdownvoltage than that normally transmitted by the ringing apparatus at thecentral office, they would not respond to the normal ringing signalstransmitted from the central office. Under such condition only the relay2| and its associated lamp would be operated. The emergency signal atthe P. B. Xs will respond only to the abnormal voltage transmitted fromP. B. X I which serves as the emergency central ofiice to establishconnections between certain pro-selected essential P. B. Xs during thetime in which those P. B. Xs are cut off from their source of ringingcurrent of normal voltage. It should be understood that the two coldcathode tubes could be replaced by a single tube provided it has thesame breakdown voltage as the two tubes, and is, therefore, capable ofpreventing the operation of the emergency ringer by the normal ringingcurrents of lower voltage.

Whil this invention has been disclosed as embodied in a particular formand arrangement of parts, it is capable of embodiment in other anddifferent forms without departing from the spirit and scope of theappended claims.

What is claimed is:

1. In an emergency telephone system the combination with a centraloflice of a P. B. X connected by a trunk to said central office, asecond P. B. X also connected by a second trunk to said central ofiice,the latter trunk being looped into said first mentioned P. B. X, aringer at said second P. B. X, a cold cathode tube connected to saidsecond trunk and said ringer to prevent the operation of the ringer bythe normal ringing voltages applied to the said trunk at the centraloffice, means at the first mentioned P. B. X to split the second trunklooped therein, and means thereat to apply an abnormal ringing voltageto that portion of the second trunk extending to the said second P. B.X, the magnitude of the said abnormal voltage being such as to cause theflow of current through the said cold cathode tube whereby the saidringer may be operated.

2. In an emergency telephone system the combination with a centraloflice having thereat a battery and also a source of normal ringingcurrent, a P. B. X located at a distance from the said central ofiice, asecond P. B. X also located at a distance from said central ofiice, atrunk connecting said second P. B. X and said central oflice and havingconnected thereto at the said second P. B. X normal signaling apparatusresponsive to the said normal ringing current, and emergency signalingapparatus responsive to a voltage greater than that of the said ringingcurrent, the said trunk being looped through the said first P. B. X, andmeans at the said first P. B. X to apply to the portion of the trunkbetween the first and second P. B. Xs a ringing current of greatervoltage than the normal ringing current to operate the said emergencysignaling apparatus.

3. In an emergency telephone system, the combination with a centraloffice of two P. B. Xs normally supplied with ringing current of normalvoltage from the central office, each P. B. X being connected by a trunkto the said central office, the trunk from one P. B. X to the centraloffice being looped through the other P. B. X, and means at the saidother P. B. X to apply a ringing-current of abnormal voltage to thatportion of the looped trunk that extends between the two P. B. Xs tobreak down a voltage-limiting device and to operate the ringer at thesaid one P. B. X whenever the connection to the normal ringing-currentsource at the said central ofiice is interrupted.

4. In a telephone system comprising a central ofiice and a plurality ofP. B. Xs, one of which is to become the emergency switching center inthe event of the destruction of the central office and the cutting offof the ringing-current normally supplied by the central ofiice to the P.B. Xs, and the trunks between the other P. B. Xs and the central oflicebeing looped through the P. B. X constituting the emergency switchingcenter, the said trunks being equipped at each of the other P. B. Xswith signaling apparatus responsive to the normal signal voltage fromthe central ofiice and also emergency signaling apparatus responsiveonly to an abnormal signal voltage, and a source of abnormal signalvoltage at the P. B. X constituting the emergency switching center tosignal the other P. B. Xs and thereby establish communication when thesource of normal ringing current at the central office fails.

5. In a telephone system, the combination with a central oiTlce of aplurality of P. B. Xs, each normally connected by a trunk to the centraloilice, one of said P. B. Xs being intended and arranged to become theemergency switching center in the event of the failure of the centraloffice to perform that function, each trunk being equipped at its P. B.X terminal with signaling apparatus responsive to the normal voltage ofthe central ofiice ringing-current, and also equipped with signalingapparatus responsive only to a voltage higher than the normal voltage,and all of said trunks looping into the P. B. X constituting theemergency switching center, and a source of the said higher voltage atthe P. B. X constituting the said emergency switching center wherebycommunication may be established between the emergency central ofiiceand each P. B. X whenever the central office supply fails.

6. A system of the type defined by claim 5 characterized by the use of acold cathode tube in series with a ringer at the P. B. X end of thetrunk which will be responsive only to a ringing voltage higher thannormal applied at the emergency switching center to the end of the trunkfrom another P. B. X looping into the said switching center.

CHARLES STANLEY RI-IOADS.

